Effects of carbide substrate properties and diamond coating morphology on drilling performance of CFRP composite

Abstract

Abstract The properties of a cemented carbide tool substrate and diamond coating were studied for the precision drilling of carbon fiber-reinforced plastic (CFRP). The microstructures and mechanical properties of WC–6 wt.% Co substrates using different WC particle sizes were examined to determine correlations between the mechanical properties and the drilling performance. The results demonstrated that WC powders with an average particle size of 2.3 μm were suitable drill substrates. Coatings of either microcrystalline diamond (MCD) or gradient nanocrystalline diamond (NCD) were deposited using hot-filament chemical vapor deposition. A drilling test using T700-grade CFRP was conducted to evaluate the drilling performance, tool wear resistance, and CFRP hole quality achieved based on the diamond coating morphology. In the CFRP drilling tests, the diamond-coated drills showed superior tool lifetimes four times longer than that of the uncoated drill. The MCD-coated drill exhibited good wear resistance compared to the gradient NCD-coated drill; however, the gradient NCD-coated drill demonstrated better machining quality in terms of the delamination factor, surface roughness inside the machined hole, and accuracy of the machining dimensions. In this study, we aimed to develop the optimal tool substrate for the drilling of general-purpose CFRP and proposed directions for the development of diamond coatings to maximize drilling performance.